Currently, an active area of technological development is the field of radiofrequency (RF) identification (ID) transponder tags. Designers of these tags envision ubiquitous usage throughout commercial, scientific and military spheres. An oft-cited advantage of RFID tags, when compared to optical barcode tags, is the relaxation of the requirement for establishment of direct line of sight between the transponder tag and its corresponding interrogation device. Another advantage of RFID tags, when compared to optical barcode tags, is the large informational space available on the transponder and the design freedom to include supplementary electronic circuitry on the RFID transponder chip to allow informational processing functions beyond simple reporting of an ID number. A further advantage of prior art RFID technologies is that the need for a power source for the informational processing functions and transmission of signals away from the ID tag is satisfied by deriving energy directly from the incoming RF interrogation signal. Said energy can be stored in an energy accumulation device within the tag to provide for short term functioning of the tag's internal mechanisms and to provide energy for an outgoing signal to the corresponding external interrogation device as described, for example, in prior art U.S. Pat. No. 5,053,774 issued to Schuermann.
The prior art describes simple informational functions resident on ID tags such as the simple reporting of a fixed number, for example as detailed in U.S. Pat No. 5,287,113. More elaborate informational functions resident on ID tags also are known such as encryption, computation, and environmental measurement as shown for example in U.S. Pat Nos. 5,532,686; 5,257,011; 6,078,251; and 6,617,963. Moreover, there is ongoing development of external information processing technology in support of RFID tags in order to better extract economic, scientific and social value from RFID technology. Examples of such external information processing include the development of RFID standardized code formats, database systems, means of allocation of RFID serial numbers and the like. Hence, the informational functions resident on the ID tags are associated with corresponding informational functions external to the tags.
Provision of an RF antenna appropriate for the intended wavelength of the RF interrogation signal is required in order to couple energy from said signal into the internal mechanisms of the RFID tag. The necessity of an antenna adds to the size, packaging complexity and cost of each tag and limits the applicability of RFID tags. Thus, there exists a need for coupling the energy of the interrogating signal into an internal energy storage device of the ID tag, without using an RF antenna, so as to minimize the size, packaging complexity and cost of said ID tag.
In the course of design and manufacture of microelectronic circuits and other microminiature devices, it is common practice to provide, in modular fashion, optionally alternative functions co-localized within the same manufactured product. Means is provided to activate, at the time of manufacture or at some later time, each option alone or in combination. Such modular construction lowers the cost of manufacture by allowing a single assembly process to produce products which serve a broad range of end user applications. A problem associated with conventional RFID tags is the lack of certainty as to which of multiple tags in proximity is actually responsive to an input signal. This lack of assurance requires human inspection to confirm tag identity. Several attempts have been made to provide a confirmatory visual signal on an activated RFID tag. Nonetheless, the broadcast nature of radiofrequency signals inevitably suffers from a lack of discrete focus. There exists a need for transponder-equipped ID tags which are manufactured with more than one means of transmission to be optionally activated, alone or in combination, at the time of manufacture or at some later time.